The present invention is concerned with a device which permits the drawing up and the delivery of liquids by means of piston pipettes to be carried out smoothly, quickly, precisely and without entrainment of liquid residues.
Serial investigations in chemical and medicinal laboratories frequently require laborious pipetting processes in which it must be ensured that even very small amounts of liquid, for example in the range of from 1 micro-liter to 5 milli-liters, can be transmitted quickly and without an excessive amount of care and concentration. The absolute exactitude and the reproducibility which can be achieved must not be smaller than those which are achieved in the measurement of large volumes, i.e., up to about 1% for the absolute exactitude and up to about 0.5% for the reproducibility. It must be possible to carry out the most varied pipetting processes rapidly and in succession without amounts of substance being entrained from the preceding measurement. When working with liquid media which pose special problems because of danger to health, for example infectious or radioactive liquids, care must also be taken to avoid human contact with those parts of the devices which come into contact with such liquids.
The devices which are commercially available and which are described, for example, in U.S. Pat. Nos. 3,606,086 and 3,815,790, certainly go a long way to meeting these requirements but, nevertheless, they still suffer from serious deficiencies. Thus, in particular, the precision and reproducibility of all the known devices leave something to be desired. Furthermore, the precisely-operating devices are laborious to use, for example, with regard to adjustment, alteration of the piston stroke and the exchange of parts of the device.
It is an object of the present invention to overcome the above-mentioned deficiencies of the previously known devices.
Thus, according to the present invention, there is provided a measuring and pipetting device with a detachable filling device attached thereto, which can be a capillary tube or an extension tip, based on the piston principle, with a device for the fixed adjustment of various stroke lengths and/or an adjusting device and/or an exchangeable piston unit, wherein the device for the adjustment of the stroke length is a tubular-shaped, stepped distance piece and/or the piston unit is exchangeably fixed with respect to a piston wire by screwing a threaded tubular bolt over a gripping collet. The adjustment device is constructed in such a manner that the piston unit and the filling device may be relatively adjusted so that when the filling device takes the form of a capillary tube, the piston tip is approximately even with a ring mark on the secured capillary tube when the piston unit is in the starting position, and when the filling device takes the form of an extension tip, the piston tip impinges against a formed stop in the secured extension tip when the piston unit is pressed through.
In the case where a capillary tube forms the filling device the distance from the starting ring mark on the tube to the capillary tube end preferably corresponds to the maximum stroke volume. The capillary tube can be secured with the help of a screw cap and of a clamping ring. The extension tip can be pushed over a sleeve with a bead and can be secured with the help of a screw cap.
The advantages which can be achieved by means of the present invention are, in particular, an extension of the field of use because of the improved and simplified adjustment and tip attachment which can be accomplished without the use of any kind of auxiliary tools. The device according to the present invention also provides an improved volume tolerance and reproducibility and its stepped construction permits a rapid volume adjustment as may be required in some uses of the device. Due to the improvements provided, the device can also be used in immulogical laboratories where it is necessary to work with especially small volumes and with a very high degree of precision. Furthermore, the danger of glass breakage and a danger of infection are substantially overcome.
For a better understanding of the present invention, one embodiment thereof will now be described in more detail, with reference to the accompanying drawings, in which: